because they could be linked somehow both of the clues go to when they both bathe and i dont mean that bathe
anywaysnotice how when the rainbow and yellow takes a bath when yellow puffle does it rainbow paint pours into the tub and they will jump in the tub and look somewhat like a rainbow puffle when they come out of tub.
and when rainbow puffles take a bath they jump in and paint starts to come off so they jump out of the tub.
and yellow puffles always did wanna be a legend so i think rainbows are just yellows covered in paint.
i rest my case :P.